JPS63103055A - Manufacture of thin iron-copper alloy strip for lead frame - Google Patents

Abstract

PURPOSE:To manufacture a thin Fe-Cu alloy strip for a lead frame having superior heat conductivity, electrical conductivity, strength and workability by continuously casting a thin Fe-Cu alloy slab having a specified compsn. consisting of Cu and Fe at a high cooling rate, cold rolling the slab and aging it under specified conditions. CONSTITUTION:A thin Fe-Cu alloy slab having a compsn. consisting of 20-90wt% Cu and the balance essentially Fe is continuously cast at >=100 deg.C/sec cooling rate. The slab is cold rolled and aged at 450-650 deg.C for 20-500min. Thus, a thin Fe-Cu alloy strip for a lead frame having required strength, supe rior heat conductivity, electrical conductivity and workability is obtd. at a low cost without especially adding other alloying elements. In case where workability is especially required, annealing at 650-1,050 deg.C for 5-60min is carried out before the aging. In case where workability and high strength are required, final cold rolling at 15-80% draft is carried out after the annealing and aging.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to an iron-copper alloy ribbon for lead frames used in low-cost semiconductor RC, LSI, etc., which has excellent thermal and electrical conductivity, strength, and workability. The present invention relates to a manufacturing method.

(Prior Art) As a lead frame material for semiconductor IC, LSI, etc., an alloy containing 26 to 30% by weight of Ni and 11 to 16% by weight of Co in iron is used, for example, as disclosed in Japanese Unexamined Patent Publication No. 59-198741. (Kovar alloy), also JP-A-60-11144
This is because alloys containing Fe and 30 to 55% Ni (42% Ni alloy is a typical component) shown in Publication No. 7 have excellent matching of thermal expansion characteristics with glass sealants and Si. It is used. On the other hand, copper and copper alloys have also gradually come to be used in ICs that require high thermal and electrical conductivity.

That is, the Kovar alloy and 42Ni alloy mentioned above have excellent strength and heat resistance, but have poor thermal and electrical conductivity, poor workability, and high cost. There is a trend toward copper alloys, which have good electrical conductivity and workability.

(Problems to be Solved by the Invention) However, copper alloys generally have poor heat resistance and strength;
Publication No. 8442 adds tin, iron, silicon, phosphorus, cobalt, etc. to improve this, but adding these increases the cost of the alloy and also causes problems such as deterioration of thermal and electrical conductivity. There was a problem.

The present invention provides thermal and electrical conductivity as a lead frame without adding other alloying elements to the iron-copper binary alloy.
The purpose of the present invention is to provide an iron-copper alloy ribbon for lead frames with improved strength and workability.

(Means for solving the problems) That is, the gist of the present invention is as follows.

(1) Ten iron-copper alloy thin slabs containing 20% by weight or more and 90% by weight or less of copper, with the balance mainly consisting of Fe.
A method for producing an iron-copper alloy ribbon for lead frames, which comprises continuous casting at a cooling rate of 0°C/sec or more, and then subjecting it to an aging treatment at 450 to 650°C for 20 minutes to 500 minutes after cold rolling.

(2) Iron-copper alloy thin slab containing 20% by weight or more and 90% by weight or less of copper, with the balance mainly consisting of iron at 100℃/
Continuously cast at a cooling rate of sec or more, and after cold rolling 650
Annealing is performed at ~1050℃ for 5 minutes or more and 60 minutes or less, and 45
A method for manufacturing an iron-copper alloy ribbon for lead frames, which comprises subjecting an aging treatment at 0 to 650°C for 20 minutes or more and 500 minutes or less.

(3) Iron-copper alloy thin slab containing 20 weight percent or more and 90 weight percent or less of copper, with the balance mainly consisting of iron at 100℃/
Continuously cast at a cooling rate of sec or more, and after cold rolling 650
Annealing is performed at ~1050℃ for 5 minutes or more and 60 minutes or less, and 45
A method for manufacturing an iron-copper alloy ribbon for lead frames, which comprises aging at 0 to 650''C for 20 minutes to 500 minutes, followed by final cold rolling at a reduction rate of 15 to 80%.

The reasons for limiting the constituent elements of the present invention will be explained in detail below.

In this invention, first, the reason for limiting the chemical composition is as follows.

The higher the content of copper, the better from the viewpoint of thermal and electrical conductivity, but if the application requires strong strength, it is desirable to increase the iron content.
Below (hereinafter referred to as -tχ), the thermal and electrical conductivity necessary for an IC lead frame cannot be obtained, so the lower limit is set to 20w.
Let it be X. The upper limit is set to 90 imtX because if the iron content is less than 10 wtX, the distribution of the iron phase, which effectively works to refine the structure, becomes insufficient.

In addition, oxygen as an impurity that is inevitably mixed in from other iron and copper raw materials is not desirable from the viewpoint of thermal and electrical conductivity, but when the amount is less than 0.03 ht%,
Since it has a small effect on electrical conductivity and also contributes to strength, it is acceptable if it is 0.03 wtX or less.

In addition, other elements are impurity elements that are unavoidably mixed into raw materials and during melting.

Next, the manufacturing method of the present invention will be explained.

In the present invention, thin slabs of iron-copper alloy are manufactured by continuous casting, and the primary cooling rate during such continuous casting is set at 100°C/sec.
Limited to c or more.

In general, the structure size after solidification depends on the cooling rate during casting, and the faster the cooling rate, the smaller the structure size and the higher the strength obtained, but the above cooling rate is necessary to obtain the desired strength of the frame. be.

The above cooling rate will be explained below. First, 90-tχ copper-iron alloy, which is the most difficult to obtain, was cast using an iron mold, a copper mold, and a twin-roll casting machine, and the casting thickness was varied to approximately 1 to 1.
Casting was performed at a cooling rate in the range ooo°C/sec. These slabs were ground to have the same thickness, heat treated at 800°C for 30 minutes, and then cold rolled to a rate of 85%. Next 480
Aging treatment was performed at .degree. C. for 500 minutes, and the Vickers hardness of 174 layers in cross section was measured to obtain the relationship between cooling rate and hardness. This is shown in FIG. From FIG. 1, the critical cooling rate at which the Vickers hardness becomes 150 or more was determined. The reason why the Vickers hardness is set to 150 or more is that this value is generally used as an index of the required strength of current lead frame materials, so this value was also adopted here. From this result, 100℃
It is clear that a Vickers hardness of 150 or more is obtained at a cooling rate of 100° C./sec or more, which indicates that a cooling rate of 100° C./sec or more is required.

Furthermore, if the copper content is 70 wt% or less, or if the cold rolling reduction in the previous stage is 50% or more, measures are required to prevent cracking during cold rolling. An effective method for this is slow cooling after casting and reheating after once cooling to room temperature. Although the effect is greater as the time increases, the heating time is set to 60 minutes or less in order to reduce coarsening of grains and decrease in the supersaturation degree of iron and copper due to rapid cooling. This effect prevents the formation of residual austenite or martensite that occurs during cooling after casting, or softens iron by tempering.
This is due to reducing the hardness difference between copper structures.

Furthermore, cold rolling and aging are subsequently performed. The main purpose of cold rolling is to obtain the thickness required for lead frames.
The reduction rate in the first stage of cold rolling determines the conditions under which the desired sheet thickness strength and workability can be obtained, depending on the combination of chemical composition, casting thickness, and final cold rolling process. The effective rolling reduction range is 30-95%.

Aging treatment is essential to the manufacturing process in order to improve thermal and electrical conductivity, and an appropriate temperature should be selected depending on the chemical composition and pre-process conditions, but in general, the lower the temperature, the better the properties. Although it is easy to obtain, if the temperature is too low, the precipitates will have a strain field around the parent phase, which will deteriorate the properties and increase the heating time, resulting in poor equipment and production efficiency.

In addition, if the temperature is too high, good properties will not be obtained because sufficient analysis will not occur, and the precipitates will become coarser, creating a disadvantageous condition for ensuring strength, so the suitable conditions are 450-650℃
The conditions for obtaining good characteristics are 20 minutes or more and 500 minutes or less in a temperature range of .

In addition, if workability is particularly required for the lead frame, cold rolling can be achieved by annealing at a temperature range of 650 to 1050°C for a practical time of 5 minutes to 60 minutes before aging treatment. 4. Removal of machining distortion and recrystallization
It is possible to improve processability by grain growth.

Furthermore, if workability and high strength are required for the lead frame, after the above annealing, cold rolling is performed for 15 to 8
Strength is increased by applying processing strain to the recrystallized structure at a rolling reduction of 0%.If the rolling reduction is less than 15%, the contribution to strength is small, and if it is more than 80%, the thermal and electrical conductivity will be significantly reduced. Therefore, this range is used.

(Example) The effects of the present invention will be explained below using examples.

Example 1 Alloy A-F (A, F
(Comparative Example) was made into 3 x 10” using a twin roll casting machine.
Continuous casting was performed at a cooling rate of 'C/sec to obtain a thin slab with a plate thickness of 2.0 mm, and then the following treatments were performed.

After electroforming, the thin slab once brought to room temperature was held at 800℃ for 30 minutes to prevent cracking during cold rolling. It was made into a cold rolled sheet.

Furthermore, aging treatment was performed at 480° C. for 200 minutes and air-cooled.

Next, the electrical resistance of the obtained sample was measured, and the evaluation of thermal and electrical conductivity was expressed as electrical conductivity (%IACS). Further, the strength and elongation were determined by performing a tensile test at room temperature using a JIS No. 13 B test piece.

The results are shown in Table 2 along with comparative examples. As is clear from this result, in the alloy B-E of the present invention, 50 kgf/a
It exhibits a strength of more than m” and an electrical conductivity associated with copper content,
On the other hand, regarding A and F, it is clear that A has excellent strength but lacks electrical conductivity, and F has good electrical conductivity but low strength.

Example 2 An alloy having the chemical composition of C listed in Table 1 of Example 1 was cast in a copper mold with a thickness of 2.0 mm at a cooling rate of about 50°C/sec. Processing was performed under the same subsequent conditions, and the same evaluation was performed.

The results are shown in Table 3. As is clear from these results, it is clear that it is difficult to obtain strength when the cooling rate during casting is slow as this, and furthermore, the electrical conductivity is also a low value when the cooling rate is slow.

Example 3 An alloy having the chemical composition of C listed in Table 1 of Example 1 was cast and cold rolled under the same conditions as in Example 1, and the aging treatment temperature was 400'C and 700'C at 200°C. The results are shown in Table 4. The results are shown in Table 4.

As shown in Table 4, it is clear that if the aging temperature is too low, good electrical conductivity cannot be obtained, and if the aging temperature is too high, the electrical conductivity and strength deteriorate.

Example 4 An alloy having the chemical composition of C listed in Table 1 of Example 1 was cast and cold rolled under the same conditions as in Example 1, and annealed at 950°C for 30 minutes before aging treatment. The samples were aged at 480° C. for 200 minutes, air cooled, and evaluated in the same manner as in Example 1. C of Example 1 is shown in Table 5 as a comparative example.

From these results, it is clear that annealing slightly decreases strength but improves elongation and electrical conductivity.

豐 Example 5 The sample subjected to the aging treatment in Example 4 was further subjected to cold rolling at a reduction rate of 50% and evaluated in the same manner as in Example 1. Table 6 shows the present invention of Example 4 as a comparative example. It was shown to.

From this result, it is clear that by further performing cold rolling of about 50% after annealing and aging, it is possible to secure the necessary elongation and improve the strength of the lead frame. The decrease in electrical conductivity is minute.

(Effects of the Invention) As explained in detail above, the present invention utilizes a combination of the specific chemical composition of iron and copper, the effect of rapid cooling, and post-processing to create an IC lead frame without adding any other alloying elements. This is a method for producing a low-cost lead frame river iron copper alloy ribbon that has the necessary strength as a material and has excellent thermal and electrical conductivity and workability, and is an industrially and economically excellent method. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between cooling rate and Vickers hardness.

Claims (3)

[Claims] (1) Iron-copper alloy thin slab containing 20% by weight or more and 90% by weight or less of copper, with the balance mainly consisting of iron at 100℃/
Continuous casting at a cooling rate of sec or more, and after cold rolling 450
A method for producing an iron-copper alloy ribbon for lead frames, which comprises subjecting an aging treatment to ~650°C for 20 minutes or more and 500 minutes or less. (2) Iron-copper alloy thin slab containing 20% by weight or more and 90% by weight or less of copper, with the balance mainly consisting of iron at 100℃/
Continuously cast at a cooling rate of sec or more, and after cold rolling 650
Annealing is performed at ~1050℃ for 5 minutes or more and 60 minutes or less, and 45
A method for manufacturing an iron-copper alloy ribbon for lead frames, which comprises subjecting an aging treatment at 0 to 650°C for 20 minutes or more and 500 minutes or less. (3) Iron-copper alloy thin slab containing 20% by weight or more and 90% by weight or less of copper, with the balance mainly consisting of iron at 100℃/
Continuously cast at a cooling rate of sec or more, and after cold rolling 650
Annealing is performed at ~1050℃ for 5 minutes or more and 60 minutes or less, and 45
A method for manufacturing an iron-copper alloy ribbon for lead frames, which comprises aging at 0 to 650°C for 20 minutes to 500 minutes, and then final cold rolling at a reduction rate of 15 to 80%.